@ThomasDunning Hi Thomas. Fare details can be found here Dublin-Belfast is route 801A

All Bus Éireann’s current route fares can be found using this application by entering the route number and the origin & destination points. In addition to the fares within a route, the Fare Finder may display some through fares to points on our national integrated network that involve onwards travel on to connecting services. Always check the Bus Éireann Journey Planner before travel. The Fare Finder displays both the full fare and an automatic potential discounted internet fare. Please note however, that not all points are available for online purchase. The Fare Finder will not include any ‘Special Offer’ fares that may be available from time to time. Click here for Bus Éireann Fare Finder Please note that premium fares apply on route X33. Free Travel passes are not valid for travel on route X33.